The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known spark ignition engines introduce a fuel/air mixture into each cylinder which is compressed in a compression stroke and ignited by a spark plug. Known compression ignition engines inject pressurized fuel into a combustion cylinder near top dead center (TDC) of the compression stroke which ignites upon injection. Combustion for both spark ignition engines and compression ignition engines involves premixed or diffusion flames controlled by fluid mechanics.
An engine configured for spark ignition combustion can be adapted to operate in a homogeneous charge compression ignition (hereafter ‘HCCI’) combustion mode, also referred to as a controlled auto-ignition combustion mode, under predetermined speed/load operating conditions. The HCCI combustion mode comprises a distributed, flameless, auto-ignition combustion process that is controlled by oxidation chemistry. An engine operating in the HCCI mode has an intake charge that is preferably homogeneous in composition, temperature, and residual exhaust gases at intake valve closing time. Controlled auto-ignition combustion is a distributed kinetically-controlled combustion process with the engine operating at a dilute fuel/air mixture, i.e., lean of a fuel/air stoichiometric point, with relatively low peak combustion temperatures, resulting in low NOx emissions. The homogeneous fuel/air mixture minimizes occurrences of rich zones that form smoke and particulate emissions.
When an engine operates in the HCCI combustion mode, the engine control comprises lean air/fuel ratio operation with the throttle wide open to minimize engine pumping losses. Air flow into the engine can be controlled by controlling opening and closing of engine intake and exhaust valves, including controlling phasing and lift of opening and closing thereof. When the engine operates in the spark ignition combustion mode, the engine control can comprise stoichiometric air/fuel ratio operation, with the throttle valve controlled over a range of positions from 0% to 100% of the wide-open position to control intake air flow to achieve the stoichiometric air/fuel ratio.